For 133.125, I collected many more relations than were needed; for more than 420M relations the filtering process has to make several passes and ends up with a significantly larger (though less dense) matrix, so 420M should be considered an absolute maximum.

For the C176 from aliquot sequence 2340 step 736 (15e sieving, 32-bit large primes), 320 million relations are enough for filtering to work with target density 120. So I'm targeting 360M relations for the C179 that I've just queued up.